Crosshole Sonic Logging (CSL) is a method to verify the integrity of drilled shafts and other concrete piles and determine soundness of concrete within the drilled shaft inside of a rebar cage providing structural reinforcement of the drilled shaft. (See, for example, American Society for Testing and Materials, ASTM D6760-08, Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing, which is incorporated herein by reference.)
CSL involves use of steel or plastic tubes installed in the drilled shaft and tied to the rebar cage. After the shaft is drilled, and before the rebar cage is placed in the hole, plastic or steel tubes are attached to the interior of the rebar cage, and then the cage is lowered into the hole and the concrete is placed. The tubes are filled with water as an intermediate medium. After curing for 3-7 days, a sound source and receiver are lowered, maintaining a consistent elevation between source and sensor. A signal generator generates a sonic pulse from the emitter which is recorded by the sensor. Relative energy, waveform and differential time are recorded and logged. This procedure is repeated at regular intervals throughout the pile and then mapped. By comparing the graphs from the various combinations of access tubes, a qualitative idea of the soundness of the concrete throughout the pile can be gleaned.
CSL is required by most departments of transportation (DOTs) and transmission line owners for quality control of drilled shaft construction. Current practice is to add 1½″ or 2″ inner diameter (ID) tubes for instrumentation access throughout the length of the drilled shaft. There are typically 3 to 8 CSL access tubes per drilled shaft. Generally, one CSL access tube may be used per foot of diameter of the drilled shaft. Each drilled shaft tested using CSL requires access tubes. In known techniques, smooth PVC or steel pipe is used to create the sonic access tubes for the CSL logging instrument which travels the entire length of the drilled shaft. Reports of debonding of the PVC or smooth steel pipe are known to occur.
Accordingly, it would be desirable to provide access tubes for CSL and/or other integrity test that overcome the above-noted problems and provide further advantages in drilled shaft reinforcement and integrity testing.